1. Field of the invention:
The present invention relates to a torque variation absorbing device for an engine.
2. Description of the prior art:
An engine for an automobile or an aircraft is equipped with a torque variation absorbing device for power transmission.
The prior art offers such a torque variation absorbing device as disclosed, for instance, in Japanese patent publications Nos. SHO 55-20930, SHO 55-20964 and SHO 56-43176. Referring to FIG. 7, a device of the prior art has two inertia members, i.e., a driving plate 101 which is connected to a crankshaft of an engine and a flywheel 102 which is connected to the follower means and is rotatable with respect to the driving plate. Between the driving plate 101 and the flywheel 102, a spring mechanism 103 and a damping and torque limiting mechanism 104 are installed. In this device the rotation of the crankshaft is transmitted to the flywheel 102 through the driving plate 101, the spring mechanism 103 and the damping and torque limiting mechanism 104. Thus the torque variation is absorbed by the vibration system of these members. A gap 105 is provided between the driving plate 101 and the flywheel 102.
Flywheel 102 is divided into the flywheel body 102a and the driven plate 102b in order to house the damping and torque limiting mechanism. The flywheel body 102a and the driven plate 102b are fastened together by a fastening bolt 107 which is screwed into a bolt hole 113. The bolt hole 113 provided in the driven plate 102b is a blind one. In other words, the bolt hole 113 does not penetrate the driven plate 102b and does not reach the frictional member 106. The frictional member 106, slidably compressed with a certain force between the driven plate 102b of the flywheel 102 and the driving plate 101, develops a frictional force when it acts.
In the conventional device, however, the abraded dust generated when the frictional member 106 gets worn, remains on the frictional surface without being removed, with the result that the frictional force developed is unstable and sometimes excessive.
A friction generating mechanism of a conventional torque variation absorbing device consists of a frictional member 106 of phenol resin or asbestos interposed between iron pieces and when a load is imposed, the mechanism generates a dry frictional resistance.
The frictional member of asbestos has a high coefficient of friction and can generate an ample frictional resistance but lacks in anti-wear property and is likely to have large fluctuations in the coefficient of friction when it is abraded. Also, the frictional member of phenol resin has a low coefficient of friction with small variations in the value under abrasion, but it is likely to get worn and lacks in durability.
Moreover, the conventional spring seat 108 is formed such that both the contact portion for contacting the driving member (flat members 109, 110) and the contact portion for contacting the driven member (driven plates 111, 112) possess an identical shape having a semi-circular projection 108a, but when a vehicle runs, the projection 108a in contact with the driven member (driven plates 111, 112) of the spring seat 108 wears so heavily that a spring 103 comes into direct contact with the peripheral member, thereby destabilizing the hysteresis torque, and the torque variations cannot be well absorbed.
Conceivably these problems will be reduced (a) when the driven plate is fabricated thicker or (b) when the semi-circular part of the spring seat is elongated in the circumferential direction. However, other problems such as increase of an axial dimension in the case of (a) and decreased strength of the driven plate in the case of (b) will occur.